3l6 VERRILL , 



the deep sea, of numerous more or less intermediate genera, the 

 limits of such groups, as well as those of recognized families and 

 genera, have become more and more indefinite. Probably future 

 discoveries will make them even more so. 



Still it is convenient to recognize subfamily groups, even if not 

 always closely definable by any one or two characters. It is the 

 combination of several characters that counts most in all the larger 

 groups. 



ANALYTICAL TABLE OF NORTHWEST AMERICAN SHALLOW- 

 WATER GENERA OF ASTR0PECTINID;E. 



Marginal plates thick, convex, spinulose on the whole surface; separated 

 by deep sutural grooves, which are usually bordered by many rows 

 of fine fasciolated spinules. Interactinal plates, when present, 

 convex, spinulose, pseudopaxilliform, and fasciolated. 



A. Marginal plates of both series large; lower ones mostly much prolonged, 



reaching the adambulacrals. Dorsal plates are true columnar 

 paxillse; interactinal plates few or none. Rays elongated. 

 Astropecten (restricted). 



AA. Lower marginal plates are not so much prolonged adorally. Inter- 

 actinal plates are in rows, forming a triangular area. 



B. Dorsal plates form convex pseudopaxillae with stellate bases : interactinal 



plates are flat or convex pseudopaxillae, in three or more paired 

 rows, with an odd interradial row; not evidently imbricated; 

 lower marginal plates are about equal in length to two adambula- 

 crals; spinose centrally. Rays rather long. Marginal fasciolated 

 grooves are simple and narrow. Adoral marginal adambulacral 

 spines are deep in the grooves. 

 Bunodaster. Type, B. rittert Verrill. 



BB. Dorsal plates are true columnar paxillae or parapaxillae. 



C. Lower marginal plates are usually spinose and spinulose, as in Astropecten. 



Rays elongated. 

 Astropectinides Verrill. Type, A. mesacutus (Sladen). Antarctic. 

 CC. Marginal plates not spinose, but covered with minute spinules ; sutural 

 grooves wide and deep. Rays short or rather short. Odd actinal 

 interradial plates are present. 



D. Marginal plates short and about equal in number to the adambulacral 



plates ; upper ones much smaller than the lower ; both series 

 become oblique distally, the sutures slanting adorally. Actinal 

 plates have a raised center, or carina, and strong lateral fascioles. 



Leptychaster Smith. Type, L. kerguelenensis. 



DD. Marginal plates few, large, subrectangular, subequal in breadth, each 



about as long as two adambulacrals : grooves wide, not notably 



oblique distally. Interactinal plates fasciolated, in three or more 



rows, rounded, convex, tabulate, not carinate ; a few unpaired ones. 



Glyphaster. Type, G. anomalus C Fisher). 



